Method of balancing very small rotating objects using air jet acceleration

ABSTRACT

A system of balancing extremely small rotating devices is described. The device to be balanced is mounted on its own axes and rotated at a high rotational speed driven by an air blast. By this means only the device being balanced is rotated and the mass of fixtures need not be considered. The amount of imbalance is measured and a laser beam is used to remove a portion of the rotating device to reduce the imbalance.

U WLU TEE 317279027 United States Patent 1 1 1111 3,727,027

Kaiser et al. 1 51 Apr. 10, 1973 [54] METHOD OF BALANCING VERY 3,621,180'11/19'71 Rolff ..219/121 L SMALL R TA I OBJECTS USING 3,663,795 5/1972Myer "219/121 L AIR JET ACCELERATION 3,499,136 3/ 1970 Nunnikhoven eta]. ..2l4/121 LM [75] Inventors: Willard D. Kaiser, Grove City;

E -J. v. T h Charles W. Rodman, Columbus, "mary mmer ru e AssistantExaminer-George A. Montanye both of Ohm Attorney-Roland A. Anderson [73]Assignee: The United States of America as represented by the UnitedStates [57] ABSTRACT Atomic Energy Commission A system of balancingextremely small rotating.

[22]. Filed: 1971 devices is described. The device to be balanced is[21] Appl. No.: 127,902 mounted on its own axes and rotated at a highrotational speed driven by an air blast. By this means only 52 us. Cl..219/121 LM, 73/461 the device being balanced is mated and the mass of51 1m. (:1. ..B23k 9/00 fixtures need be cnsidered- The amum [58] Fieldof Search ..219/121 L, 121 EB; balance is measured and a laser beam isused 2 4/22 23; 415 202. 74/543; 73/4614 3 remove a portion of therotating device to reduce the imbalance. [56] Reiereilces cued 1 Claim,5 Drawing Figures UNITED STATES PATENTS 3,076,342 2/1963 Hilgers..'73/462 A1955? (H/C? C/vW/FGE 57??035 FIRE H5. fl/r? CONT/FOL 15,0/315. A/a lac /0 LOCKED i w /y- L/D LOCK PRESsU/FE r/gi Z Z F/RE [WE 9SPEED 5/ 650 F PEGULflTO/i j l i C/ficU/r a 577i061E I a 10, i5MBA/James TWESHOLD MEHSURE Mensa/ms SENSOR SPEED .SP'ED flaw/v02 4'19FORCE I i y Fllj f? 7* r0- T/P/l/VSDUCER L i/l sen 50R 0/615PATENTEDAPMOWR 3,727, 2.?

sum 2 or 4 2 aiwc y PATENTEU APR 1 19 3 SHEET 3 BF 4 METHOD OF BALANCINGVERY SMALL ROTATING OBJECTS USING AIR JET ACCELERATION CONTRACTUALORIGIN OF THE INVENTION The invention described herein was made in thecourse of, or under, a contract with the US. ATOMIC ENERGY COMMISSION.

BACKGROUND OF THE INVENTION It is often necessary to balance rotatingparts of a system in order to achieve desired stability and accuracy.Conventional methods of balancing have included the mounting of thedevice to be balanced in special chucks and rotating the device rapidlyto determine the amount of imbalance and the location of the imbalance.Where very small parts are involved the use of chucks or other fixturesto hold the rotating part contributes an appreciable mass which mayitself be imbalanced. Further, the eccentricity of the axis of therotating chuck contributes to errors. Balancing devices of this typehave achieved a resolution of the order 1 gram which is accurate formany purposes. However, where the device which is to be balanced has amass of the order of 1 gram it is necessary to use other methods forbalancing.

Hand balancing has been successfully used for balancing extremely smallparts. The device is mounted on a poise and rotated to find the heaviestportion. Material is moved from the heaviest portion to improve thebalance. Thisis continued until the required degree of balance isachieved. This hand balancing is slow, tedious and limited in itsaccuracy.

It is therefore an object of this invention to provide an improvedsystem for balancing extremely small rotating masses.

Another object of this invention is to provide a system for balancingvery small rotating masses in which the balancing procedure can beaccomplished automatically or semiautomatically.

Another object of this invention is to provide a system for balancingvery small rotating devices in which only the device being balanced isrotated.

SUMMARY OF THE INVENTION In practicing this invention, the object whichis to be balanced is mounted in bearings and spun by a jet of air. Theobject to be balanced is brought to a speed greater than the measuringspeed and the jet of air is shut off. The rotating object is permittedto coast to the measuring speed and the amount of imbalance is measuredby a transducer to which the bearings supporting the rotating object arecoupled. The object then coasts to a lower balancing speed at which asmall portion of the object is removed.

A laser is mounted and aimed at the rotating object. The laser firingcircuit is synchronized with the imbalance force measured by thetransducer so that a small portion of the object can be removed byfiring the laser. The laser is triggered at the appropriate point intheobjects revolution in order to decrease the amount of imbalance forcepresent. After firing, the rotating object is permitted to achieveequilibrium and is then accelerated to speed by the jet of air to repeatthe cycle. A strobe unit can be used in conjunction with the laser inorder to permit changing of the point at which a portion of the objectis removed to achieve balance.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in thedrawings, of which:

FIG. 1 is a view of the object being balanced together with themechanical structure of the mounting and laser;

FIG. 2 is an enlarged drawing of the objects mount ing structure;

FIG. 3 is a curve showing the points at which the various operationstake place;

FIG. 4 is a block diagram showing the structure by which the imbalanceforces are measured and the laser or strobe is fired; and

FIG. 5 is a block diagram of the logic system for controlling themeasurement and firing of the laser.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, there isshown the structure of the balancer. A verge 10 is the object which isto be balanced in this example. Verge 10 has a mass of approximately 1gram and in order to achieve balance only a very small mass can beremoved from the verge. The verge is supported in bearings mounted on asupport assembly 11 which, in turn, is mounted on a transducer 13. A jetof air is supplied through needle 14 and air hose 16 and impinges on theverge 10. The air jet causes verge 10 to rotate. The support assembly 11and transducer 13 are mounted on a block 18 which, in turn, is supportedby isolation springs 17.

The control circuitry is mounted in a controlunit 20 and the laser unit21 is connected to the control unit 20. Laser unit 21 includes a laser23 which is aimed at verge 10. Laser unit 21 may also include a strobeunit 24 timed to fire in synchronism with laser 23 in order that thepoint at which the laser will strike the rotating verge may beascertained.

The laser structure and verge mounting structure shown in FIG. 1 isenclosed in a cabinet with interlocks (not shown). This is a safetyfeature, as the laser beam can be highly destructive to operators whoare not properly shielded. As will be subsequently described, theinterlock features prevent firing of the laser unless the cabinet isclosed and locked.

Referring to FIG. 2, there is shown an enlarged drawing of the supportassembly 11 mounted on transducer 13. The verge support assembly whichis removable for ease of installing and removing verges consists of apair of sapphire jewel bearings 26 which are mounted on a V-groove ofthe support assembly 11. The sapphire bearings 26 are held in positionby spring clips 27 L Referring to FIG. 3, there is shown a plot of theverge rotation speed versus time. At point A the verge has been rotatedunder a low speed air jet and at this point the high speed air jet isturned on and the verge starts to accelerate to its maximum speed. Atpoint B, the high speed air is turned off and the verge starts to losespeed. At point B, when the high speed air is turned off, the laserenergy storage capacitors start charging. At point B, the charging hasbeen completed and the laser is enabled for firing. At point C, themeasure speed threshold sensor generates a signal consistingof a stepchange from 0 to 1 if the magnitude of theverge imbalance is less than apredetermined amount. If the verge is not balanced, the signal remains azero. As the speed continues to decrease, it passes through thebalancing speed, point D of FIG. 3, and a 1 signal is developed by acircuit to be subsequently described. When this occurs, a pulse enablingthe laser is developed. This insures that the triggering of the laserdoes not occur during acceleration of the verge but only duringdeceleration. At a particular time during the enabling pulse a firingpulse is developed to fire the laser. The enabling pulse developed is ofsufficient duration to insure that more than one revolution of the vergewill occur while the enabling pulse is present. This permits the pointat which a portion of the verge is removed to achieve balance to beselected as desired. At point A, the high speed air is again turned onand the cycle is repeated until balance is achieved.

Referring to FIG. 4, there is shown a block diagram of the balancingsystem and the measuring system used in this invention. The verge 31which is to be balanced is mounted on bearings 32 attached to apiezo-type force transducer 34. Air from a pressure regulator 35 isdirected by air pipe 37 against the verge to rotate the verge. Pressureregulator 35 has a high speed air and a low speed air adjustment whichcan be turned on and off by the logic circuitry, as will be subsequentlydescribed. The rotating verge can be illuminated by a strobe 39 in orderto determine the spot 40 at which the laser beam will remove material.The spot at which material is to be removed can be selected in a mannerwhich will be described. Laser 41 is also directed against spot 40 whenit fires.

The above-described mechanism is contained in a cabinet 43 which islocked by a lid lock mechanism 44. Other parts of the mechanism can bewithin the cabinet 43 or outside as desired.

Force transducer 34 produces a sine wave as verge 31 rotates. This sinewave is at the frequency of the rotating verge and the signal isamplified by amplifier 46. The signal is filtered by bandpass filter 47to remove unwanted frequencies and the filtered signal is applied to aplus to minus sensor 49, imbalance threshold sensor 50 and imbalanceamplifier circuit 51. Bandpass filter 47 attenuates frequencies greaterthan the frequency of the signal developed by the rotating verge of themeasuring speed and less than the frequency of the signal developed bythe rotating verge at the balance speed.

The plus to minus sensor 49, senses the point at which the sine wavesignal from filter 47 goes through zero in a plus to minus direction anddevelops an output pulse at this point. Imbalance threshold sensor 50develops an output pulse when the magnitude of the imbalance is below apredetermined amount. The output of the imbalance amplifier circuit 51is applied to a fire speed circuit 53 and measure speed circuit 54. Firespeed circuit 53 is responsive to the frequency of the imbalance signalto develop an output pulse when the frequency of the signal shows thatthe rotating object has reached the fire speed. In a similar manner,measure speed circuit 54 acts to develop an output pulse when the speedof the rotating object reaches the measuring speed.

Referring to FIGS. 4 and 5, the operation of the logic circuit whichdevelops the proper signals to operate the device will be described. Theoutput of the plus to minus sensor 49 is coupled to inverter 60 andthrough selector switch 61 to monostable multivibrator 63. Selectorswitch 61 can be used to select the desired phase of the cycle signalfrom plus to minus sensor 49. The cycle signal acts to trigger themonostable multivibrator 63 and the trailing edge of the pulse producedby monostable multivibrator 63 acts to trigger monostable multivibrator65. Resistor 64 is used to vary the length of the pulse from monostablemultivibrator 63. Since the monostable multivibrator 63 is triggered atthe zero point in the cycle of signal developed by force transducer 34of FIG. 4 by varying the length of the pulse from monostablemultivibrator 63, the point in the rotational cycle of the rotatingobject at which monostable multivibrator 65 is triggered can be variedover a range of 180. By selecting the proper phase by selector switch61, the point at which monostable multivibrator 65 develops an outputsignal can be varied over a range of 360 in the rotation of the verge.

To start the cycle of operation, the low speed air control is operatedto turn the low speed air on and start rotation of the verge 31. Theoperation of the verge can be observed and the test setup checked. Thecabinet is closed and the lid locked with the lid lock control 71. Thecycle control 72 is operated and a signal is transmitted to AND gate 74.The inputs to AND gate 74 from low speed air control lock lid, control71 and cycle start 72 develop an output signal which sets fiipflop 75.Flipflop 75 then develops an output which sends an enabling signal toAND gate 76 and AND gate 78. With the lid locked, a lid lock signal isreceived from lid lock control 44 and is used as an enabling signal forAND gate 76 and the laser fire AND gate 80. The set output of flip-flop75 is also coupled to high speed air timer 82 to start the operation ofthis air timer.

The operation of the high speed air timer 82 sends a signal to thepressure regulator 35, turning on the high speed air to accelerate theverge 31. An inhibit signal is also applied to AND gate 76 to preventthe laser capacitors from charging.

At the end of the high speed air cycle, the verge is rotating at a highrotational speed greater than the measuring speed or the laser firingspeed. Timer 82 turns off the high speed air and the verge is thenpermitted to coast down to a lower speed. When the high speed air isremoved, the inhibiting signal is removed from AND gate 76 and the lasercapacitors are charged.

As the verge rotation shows, the point is reached at which the measurespeed signal is generated by measure speed circuit 54 and is coupled tothe monostable multivibrator 83. Monostable multivibrator 83 developesan enable signal which is applied to AND gate 84. AND gate 84 alsoreceives an enabling signal from time delay 85. With the high speed airsignal off, an inhibiting signal is removed from AND gate 84. At thispoint, if imbalance threshold detector 50 develops an output signalindicating that the amplitude of the imbalance is below a predeterminedamount, an enabling signal is received by AND gate 84. If the magnitudeis grater than the predetermined amount, no enabling signal is received.If the verge is balanced at this point, AND gate 84 develops an outputsignal which is coupled to AND gate 78. AND gate 78 then develops anoutput signal which returns flip-flop 75 to its reset position, endingthe balancing cycle. Balance complete control 87 can also resetflip-flop 75 to end the cycle of operation' If the magnitude of theimbalance is greater than the predetermined amount, the sequencecontinues and the verge coasts downward until the fire speed is reached.When the fire speed is reached, a signal from fire speed detectingcircuit 53 is coupled to monostable multivibrator 88 to develop anoutput signal which is coupled to AND gate 90. At the predeterminedpoint in the cycle, AND gate 90 receives a firing signal from monostablemultivibrator 65. An enabling signal from time delay 85 and a firesignal from laser control 91 are also applied to AND gate 90. With thehighspeed air turned off, the inhibiting signal to AND gate 90 isremoved and AND gate 90 develops an output signal which is applied totime delay 85 and AND gate 80. Laser control 91 and strobe control 94are mechanically interlocked so that only one can be operated at a time.With laser control 91 operated supplying an enabling signal to AND gate90 and a disabling signal to the strobe AND gate 93, strobe control 94is inoperative and the disabling signal to AND gate 80 is not present.The AND gate 80 then develops a firing signal which is applied to thelaser 41 to fire the laser. The output signal from time delay 85 isremoved and AND gate 90 is disabled immediately after the laser firingsignal is produced. This prevents a laser firing signal from beingdeveloped for a period of time after the laser has been fired. Thispermits the verge to settle and recover from the impact of the laserbeam before further measurements and firing are accomplished. This timedelay signal from time delay 85 is also removed from AND gate 84 whichcontrols the measuring speed.

If it is desired to operate in the strobe mode, strobe control 94 isoperated. This turns off laser control 91 and a disabling signal isapplied to the laser AND gate 80 and an enabling signal is applied tothe strobe AND gate 93. In the strobe mode the firing signal frommonostable multivibrator 65 is applied to AND gate 93 every cycle and astrobe firing signal is applied to the strobe unit 39. Strobe 39 acts tostop the rotation of the verge and show the point at which the laserbeam will impact.

By rotating the verge to a high speed and then permitting the verge tocoast downward in speed through measuring and firing speed ranges, moreaccurate measurement and balance procedure is obtained. The interlockingcontrols prevent measurement and laser firing for a predetermined periodof time after a laser has fired so that the impact forces of the laserare not upsetting to the measuring process. Also, with the high speedair turned off during the measurement and firing process, thedisturbances caused by the blast of air are not present at these times.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. The method of dynamically balancing an imbalanced rotatable objectwhere said object is very small having a mass on the order of 1 gram,including the steps of:

a. rotating said rotatable ob ect to a predetermined speed with a firstmotive force from an air jet; decelarating the speed of rotation of saidobject by removing said first motive force from said object whilemaintaining a second motive force upon said object with said secondmotive force being less than said first motive force thereby allowingthe speed of rotation of said object to drop successively to a measuringspeed and a balancing speed;

c. measuring with a force transducer the magnitude of said imbalancewith said object at said measur ing speed;

d. developing a laser firing signal corresponding to the location andfrequency of said imbalance with said object at said balancing speed andwith said magnitude of imbalance measured at said measuring speedgreater than a predetermined amount;

e. firing a laser at said object at the point of imbalance in responseto said laser firing signal with said object at said balancing speed,thereby removing a portion of said object;

f. continuing automatically the balancing sequence of steps (a) through(e); and

g. automatically stopping the balancing sequence with said magnitude ofimbalance below a predetermined amount.

1. The method of dynamically balancing an imbalanced rotatable objectwhere said object is very small having a mass on the order of 1 gram,including the steps of: a. rotating said rotatable object to apredetermined speed with a first motive force from an air jet; b.decelarating the speed of rotation of said object by removing said firstmotive force from said object while maintaining a second motive forceupon said object with said second motive force being less than saidfirst motive force thereby allowing the speed of rotation of said objectto drop successively to a measuring speed and a balancing speed; c.measuring with a force transducer the magnitude of said imbalance withsaid object at said measuring speed; d. developing a laser firing signalcorresponding to the location and frequency of said imbalance with saidobject at said balancing speed and with said magnitude of imbalancemeasured at said measuring speed greater than a predetermined amount; e.firing a laser at said object at the point of imbalance in response tosaid laser firing signal with said object at said balancing speed,thereby removing a portion of said object; f. continuing automaticallythe balancing sequence of steps (a) through (e); and g. automaticallystopping the balancing sequence with said magnitude of imbalance below apredetermined amount.